Ethyl azidoformate, decomposition

The photolytic and thermolytic decomposition of azides in the presence of olefins has been applied to aziridine synthesis. However, only a limited number of steroid aziridines have been prepared in this manner. The patent literature reports the use of cyanogen azide at ca. 50° for 24 hours in ethyl acetate for the preparation of an A-nor- and a B-norsteroidal aziridine. The addition is believed to proceed via a triazoline. The reaction of cholest-2-ene with ethyl azidoformate takes place in a nonselective manner to produce a mixture of substances, including C—H insertion products. 

Careful chromatographic and detailed HNMR spectroscopic analysis of the products from the thermolyses of ethyl azidoformate in o-, m- and p-xylene revealed in all cases a mixture of 1 //-azepines.80 In o-xylene, only two of the four possible isomers were separated and characterized, namely, ethyl 4,5-dimethy 1-1 //-azepine-1 -carboxylate (9 %) and ethyl 3,4-dimethyl-l H-azepine-1-carboxylate (7 %). w-Xylene yielded a 2 3 mixture of ethyl 3,5-dimethyl-l//-azepine-1-carboxylate and ethyl 2,4-dimethyl-l//-azepine-l-carboxylate. The 2,4-dimethyl isomer (20 %) can be isolated from the mixture by removal of the 3,5-dimethyl isomer as its Diels-Alder cycloadduct with ethenetetracarbonitrile. p-Xylene gave a mixture of the two possible isomeric azepines which were partially separated by column chromatography. A pure sample of ethyl 2,5-dimethyl-1//-azepine-1-carboxylate (26%) was obtained from the mixture by selective decomposition of the 3,6-dimethyl isomer with refluxing alcoholic potassium hydroxide. 

The metalloporphyrin-catalyzed decomposition of ethyl azidoformate in the presence of an arene has been investigated but with little success in improving the yields of the 1 //-azepines.151 The nickel and copper complexes had no effect, whereas the cobalt-tetraphenylporphyrin complex accelerated the decomposition rate of the azido ester but produced more A-arylurethane rather than 1//-azepine. 

Thermal decomposition of ethyl azidoformate in the presence of 4-phenyl-l,2-dithiole-3-thione leads to 1,2,3-dithiazine (400 Scheme 51) (76CJC3879). 

Photochemical decomposition of ethyl azidoformate in cyclohexene gives 7-carbethoxy-7-azabicyclo[4.1.0]heptane (108) as main product (56% at 38° and 75% at —75°) together with the three isomeric cyclohexenylurethans.82>83M>8 A nitrene mechanism for the reaction is supported by the fact that the same products in almost the same ratio are obtained in the base-induced cleavage of N-p-nitrobenzenesulfonoxyurethan (107). All evidence indicates that the second reaction yields the carbethoxynitrene by an a-elimination mechanism. The aziridine isomerizes at 140° into 2-ethoxy-4,5-cy clo hexano-A2-oxazoline (109). 

Thermal decomposition of ethyl azidoformate in the presence of 4-phenyl-l,2-dithiole-3-thione leads to the rare 1,2,3-dithiazine system (254) (76CJC3879). The reaction presumably involves initial attack of the nitrene at S-l, followed by a [1,2] rearrangement of the resulting ylide (Scheme 34). 

Thermal or photochemical decomposition of ethyl azidoformate in the presence of mesityl oxide gave the aziridine 63, which thermolyzed in xylene to the 4-oxazoline 64.54 When 63 was heated with DMAD in... 

In contrast to these results, the photolytic decomposition of ethyl azidoformate produces a mixture of the stereospecific and the nonstereospecific addition product corresponding to 70% of the singlet and 30% of the triplet species. Interception experiments in cyclohexane point equally to a triplet component of 30% in photogenerated carbethoxynitrene... 

Ethyl azidoformate and l-trimethylsilyl-l,4-dihydropyridine react at room temperature to give the cyclic amidine 41. Since the reaction takes place 60° below the decomposition temperature of ethyl azidoformate, it is unlikely that carbethoxynitrene intervenes, formation of the triazoline followed by a Fusco rearrangement being the more reasonable interpretation. 

Reaction with benzene. Irradiation of a solution of ethyl azidoformate (I) in benzene affords N-carboethoxyazepine (4) in about 70% yield. In a study of the flash-photolytic decomposition of ethyl azidoformate, Lwowski found spectro-... 

The thermal or photolytic decomposition of carbonyl azides in the presence of dipole acceptors such as acetylenes provides a valuable method for the construction of oxazoles. Thus the reaction of ethyl azidoformate with either diphenyl- or diethylacetylene produces mainly the 2-ethoxy-oxazole (77 ).166 166 The reaction involves the 1,3-dipolar cycloaddition of carbethoxy nitrene (76b) to the alkyne to give the oxazole (77). On the... 

Exposure of the ketene acetal (300) to ethyl azidoformate for one month at —15 °C gave the J2-l,2,3-triazoline (301) which readily decomposed on warming (5 days 35 °C) to the J -oxazoline (302) when the triazoline had a 4-substituent, the decomposition took a different course e.g. (303) gave (304) after one day at room temperature. ... 

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